The present application is based on and claims priority from the following Japanese Patent Application: 2001-55352, filed Feb. 28, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a rotary electric machine, such as an AC generator, to be mounted in a passenger car or a truck or a generator-motor to be mounted in an electric vehicle or an industrial vehicle.
2. Description of the Related Art
As the rotary electric machine has become more powerful, compact and more accurate, it has unlimitedly come to use in industry and social life system. Accordingly, it has become very important for safety and life to detect a failure of the rotary electric machine so that a user can cope with the failure before an accident. For this purpose, it is necessary to provide an inexpensive, highly efficient and reliable failure detection device or system. In particular, the energy of the power system of the rotary electric machine (e.g. input side of a motor or output side of a generator) is so large that the failure may cause a terrible disaster, such as a fire. In order to prevent such a failure, the following arrangements of detecting the operation condition of the rotary electric machine have been proposed: a thermistor is inserted into a stator winding to detect abnormal temperature caused by a failure of the winding; and current transformers (CT) are respectively inserted into phase-windings of the three-phase stator winding to measure a current composite vector or difference vector so as to detect leakage of electricity or short circuit.
However, it is difficult to insert such a thermistor into the stator winding in an automatic winding process of the rotary electric machine. In addition, it is difficult to eliminate a big difference in reliability between the rotary electric machines. On the other hand, it becomes expensive to employ the current transformers in the rotary electric machine.
Therefore, a main object of the invention is to provide a reliable and inexpensive rotary electric machine whose failure can be surely detected.
According to a feature of the invention, a vehicle AC generator includes a multi-phase armature, a rotor, first means disposed in the armature for generating an output signal according to a balance condition of magnetic field of the armature winding and second means for judging whether the armature fails or not by comparing the output signal with a threshold value. Preferably, the first means includes an unbalance detection coil disposed in a portion of the armature where the unbalance detection coil is magnetically more influenced by a composite magnetic field caused by unbalance of current values of the multi-phase armature than a composite magnetic field of at least one of the rotor and the armature. The second means may be comprised of an alarm circuit for outputting alarm if the output signal of the first means becomes larger than the threshold value.
It is also preferable that the unbalance detection coil has a winding pitch that is equal to the quotient of the pole pitch divided by an odd number and is an even number of times as long as the winding pitch. The unbalance detection coil may be disposed in parallel with the stator core along coil ends of the armature winding.